Zinc base casting alloy



United States Patent 3,420,661 ZINC BASE CASTING ALLOY Leslie J. Larrieu, San Marino, Caiifi, assignor to Morris P. Kirk & Son, Inc., Los Angeles, Calif., a corporation of Nevada No Drawing. Filed May 4, 1966, Ser. No. 547,407 US. Cl. 75-178 12 Claims Int. Cl. C22c 17/00 ABSTRACT OF THE DISCLOSURE Improved zinc base die casting alloys conforming to A.S.T.M. specification Alloy XXIII and Alloy XXIII modified with small additions of nickel, both alloys improved in mechanical strength retention after aging by the addition of small but critical amounts of beryllium.

Percent Copper (max.) .25 Aluminum 3.5-4.5 Magnesium .02.05 Iron (max.) .10 Lead mam) .005 Cadmium (max.) .004 Tin (max) .003 Zinc Remainder The A.S.T.M. Alloy XXIII with composition limits as listed above enjoys a very large usage in the manufacture of zinc base castings. This alloy possesses very good fluidity and castability, however, it does possess the objectionable property of losing a substantial part of its good me chanical properties, particularly, the important tensile strength property, after aging over periods of six months to five years at room temperature and after shorter intervals of time when temperatures in excess of room temperature are encountered. The mechanical properties most substantially affected are tensile strength and hardness. Impact strength is relatively unaffected by aging changes.

In like manner the A.S.T.M. Alloy XXIII, when modified by a substitution of a small amount of nickel to compensate for the use of a lower amount of magnesium, is similarly affected by loss of tensile properties after aging period at room temperature. The use of the lesser amount of magnesium is made in order to achieve better castability for the alloy and the addition of nickel to the alloy provides compensatory corrosion protection.

It is well known by those informed about zinc alloy metallurgy that the binary alloy of zinc-aluminum, con taining 3.5%-4.5% aluminum and .005%.05% magnesium is subject to at least one phase change during aging. It is also well known that during that during these changes in phase relationship there occurs a substantial reduction in the amount of mechanical properties when compared to those possessed in the as cast state. Mechanical properties, chiefly tensile strength and hardness, and dimensional properties such as shrinkage and expansion are involved. The expected behaviours are a loss in tensile strength and a loss in hardness accompanied by a very slight shrinkage on the order of .006" in 6".

It is also well known that the addition of small amounts of magnesium such as .005%.05% retards the transformation and contributes both to better as cast mechanical properties and to some retention of those properties after aging.

I have discovered that the addition of small amounts of beryllium such as .-0005%-.01% to the A.S.T.M. XXIII Alloy containing aluminum 3.5%-4.3%, copper .25% max., magnesium .'02%-.05%, iron .10% max., lead. .005 max., cadmium .004% max., tin 003% max., balance special high grade zinc, either retards the phase change or strengthens the transformed phase thus producing an alloy with more retained mechanical properties after aging than an identical compositioned alloy without beryllium.

I have found that about .002% to about .005 is the optimum range for beryllium and that about 01% beryllium is the maximum amount and that a minimum amount of beryllium is about .0005%, and that about 004% is a preferred optimum amount.

Specifically, I have discovered that the range for beryllium is definitely critical in the sense that there is a minimum below which beneficial results of strength retention after aging are not obtained and a maximum above which beneficial results of strength retention after aging are not obtained in proportion to the increased amount of beryllium added.

Table A lists the retention effects of very small beryllium additions to the XXIII Alloy and Table B lists the compaartive retention effects of a .005 beryllium and .010% beryllium to the XXIII Alloy.

TABLE A.THE EFFECTS OF SMALL ADDITIONS OF BERYLLIUM TO XXIII ALLOY TABLE B.THE EFFECTS OF LARGER ADDITIONS OF BERYLLIUM TO XXIII ALLOY Composition Tensile strength in p.s.i.

aged at RT Lot Al Cu Mg Be As cast 2% yrs. 5 years The results listed in Table A confirm an indicated minimum addition of beryllium of about .0005

The results listed in Table B present a substantial sucperiority for the .01% beryllium addition for the conditions of as cast and aged 2 /2 years at room temperature, however, it is apparent that for the longer term five year period, the two beryllium additions of .005% and .01% impart about equivalent retention properties.

Additional consideration of some reduced ductility from larger beryllium additions and the cost of the alloy addition, when compared to the retention obtained, limit the maximum addition to an amount of about .0l% beryllium.

I have also discovered that the addition of small amounts of beryllium such as .0005%.010% to the A.S.T.M. Alloy XXIII modified with nickel in amounts ranging from about .005 to about .05 retards and/ or strengthens the phase and produces an alloy with more retained mechanical properties after aging than an identical compositioned alloy without beryllium. I can add nickel in the range of about .005% to about .02% with the optimum amount of about .0l%. I have found that the same optimum range, minimum amount and maximum amount of beryllium listed for Alloy )QIHI are equally applicable to the modified Alloy XXIII.

The specification for Alloy XXIII lists a maximum copper content of .25 This limit for copper was set in order to insure the preservation of minimum dimensional changes after aging and to eliminate the possibility of reduced ductility also after long term aging. These changes in ductility and dimension after aging for Alloy XXIII remain constant for copper contents up to about .40% copper and it is now felt that copper contents up to this level will not materially change the characteristics of the XXIII alloy. The .25 maximum copper in the specification amply provides for the preservation of these properties.

I have found that copper in the range of .05 to .40% possesses some increased benefit for strength retention but adds more to the retention of hardness after long term room temperature aging.

I have also discovered that even though beryllium alone exerts a substantial amount of retarding or strengthening influence on the transformation of Alloy XXIII during aging, it is the combined effect of magnesium in the range about .005 to about .05 and of beryllium in the range .0005%.01% that produces the valuable properties of mechanical strength retention after aging. And with regard to the amount of magnesium, I have discovered that intermediate amounts in the range of about .01% to about .03% may be desirable for strength retention with the optimum amount of about .02%.

The following mechanical property listings are presented in tabular form and are typical representations of the revealed discoveries. The examples present mechanical property data for various compositions within the specification tolerance of A.S.T.M. XXIII and include compositions both with and without beryllium. Also included are mechanical property data for various compositions described as a modified XXIII alloy containing small amounts of substitutional nickel for reduced amounts of magnesium.

Tables I, II, HI, VII and VIII list tensile strength properties for aging periods of 60 days and two years under normal conditions of room temperature as well as the as cast tensile properties which were obtained in all instances 24 hours after casting.

Table IV presents tensile data for an aging period of eight months at room temperature as well as the as cast tensile properties. Table V lists the longer term tensile properties after two and a half years and five years aging at room temperature as well as the as cast properties. Table VI lists the properties of impact strength and hardness obtained after the long term aging period of five years as well as the as cast properties.

TABLE I.EFFECT OF BE RYLLIUM IN THE PRESENCE OF MAGNESIUM AND THE ABSENCE OF COPPER-DIE CAST L t Composition Tensile strength in p.s.i.

Al Cu Mg Be As cast 60 days 2 years at RT at RT TABLE II.EFFECT OF BERYLLIUM IN THE PRESENCE OF MAGNESIUM AND COPPER-DIE CAST Composition Tensile strength in p.s.i. Lot

Al Cu. Mg Be As east 60 days 2 years at RT at RT TABLE III.--EFFECT OF BERYLLIUM IN THE PRESENCE OF MAGNESIUM AND NICKEL, AND THE ABSENCE OF COPPER-DIE CAST Composition Tensile strength in p.s.i. Lot

Al Cu Mg Ni Be As cast 60 days 2 years at RT at RT It is significant that the two alloys are substantially equivalent in strength properties through 60 days at room temperature and that retention superiority is substantial after two years of room temperature aging for the alloy with the .005 beryllium addition.

TABLE IV.EFFECT OF BERYLLIUM IN THE PRESENCE OF MAGNESIUM AND COPPER, AND BOTH WITH AND WITHOUT NICKEL-DIE CAST Composition Tensile strength properties Lot Al Cu Mg Ni Be As cast 8 months at RT It is significant that the nickel alloy with beryllium retains 1255 p.s.i. more tensile strength than the nickel alloy without beryllium after the moderate term aging period of eight months, however, it is even more significant that the beryllium bearing alloy without nickel retains more strength than either the nickel alloy alone or the nickel alloy with beryllium.

The following tensile strength data listed in Table V illustrates the retentive effect of beryllium upon the A.S.T.M. Alloy XXIII containing very small amounts of copper and the effects of magnesium alone at various concentrations upon retention of tensile properties after long term aging periods of two and a half years and five years at room temperature.

TABLE V.EFFECT OF MAGNESIUM ALONE AND MAGNESIUM WITH BERYLLIUM-DIE CAST Composition Tensile strength properties in p.s.i. Lot

Al Cu Mg Be As east 2% yrs. 5 years at RT at RT These mechanical property data further substantiate the improved tensile strength properties imparted to the XXIII Alloy composition with small addition of beryllium. These tensile strength properties also indicate that neither the low amount of .006% magnesium nor the high amount of .05% magnesium is as desirable from the retained strength objective as the .02% magnesium 5 addition and that 005% beryllium imparts additional strength retention over the .00l% beryllium addition.

The following comparative listing, Table VI presents the Charpy impact properties and the Brinell hardness properties for all of the alloy compositions listed in Table V and after the aging periods as designated in that table.

TABLE VI. EFFECT OF MAGNESIUM ALONE AND MAGNESIUM WITH BERYLLI'UM Composition Clrarpy impact Brinell hardness Lot Al Cu Mg Be As 5 years As 5 years east at RT cast at RT It is readily evident that impact strength is neither affected by the compositions and alloy contents listed nor by the aging time and conditions employed. This property remains good for the XXIII Alloy under most conditions of time and exposure.

The Brinell hardness properties parallel the tensile properties to some extent and it is significant to note that the two beryllium bearing alloys, 1399 and 1400, lost about 10 points Brinell each after aging five years whereas the beryllium free alloys lost a greater amount in each instance.

Many large die casting operations employ the practice of quenching the cast parts as they are ejected quite hot from the die casting machine. The usual practice is to use a water soluble oil emulsion solution. This practice constitutes a somewhat severe quench and produces somewhat superior mechanical properties for the parts in the as cast condition, particularly Brinell hardness.

Table VII presents the tensile strength properties for the XXIII Alloy containing .10% copper and .02% magnesium and the effect of .005 beryllium on that composition quenched and aged. Table VIII lists similar test results for a comparable XXIII Alloy containing .05% nickel and also quenched.

TABLE VII.EFFECT OF BERYLLIUM ON XXIII ALLOY WITH 10% COPPER-DIE CAST AND QUENCHED Composition Tensile strength properties Lot Al Cu Mg Be As cast 2 years at RT It is evident that the long term aging at room temperature reduces the as cast tensile strengths obtained from quenching down to the levels obtained for similar compositioned unquenched specimens. The superior tensile strength retention properties imparted by the beryllium addition are evident.

TABLE VIII.EFFECT OF BERYLLIUM ON XXIII ALLOY WITH .10% COPPER AND .057 NICKEL-DIE CAST AND It is evident that the presence of nickel has contributed some additional tensile properties to both the beryllium free alloy and the beryllium bearing alloy, however, it

is quite evident that the conditions of quenching and the presence of nickel do not alter the retentive properties imparted by the presence of a small addition of beryllium.

These examples and comparisons demonstrate the effect that beryllium bears upon the tensile strength of Alloy XXIII after moderate to long term periods of aging at room temperature. The observed improvement either results from retarding the rate of change and hence the total amount of change in phase relationships or the small beryllium addition imparts a strengthening eifect upon the Weaker phase produced by transformation.

Some credence can be placed in the latter hypothesis from the study of many photomicrographs depicting the microstructure of comparative compositions.

The 4% aluminum balance zinc composition is comparatively very coarse. The addition of magnesium to this composition refines the structure and produces a random constituent distribution, whereas the addition of beryllium in the presence of magnesium refines the resultant microstructure and produces a marked improvement in the homogeneity of constituent distribution. Beryllium appears to alter the microstructures by dispersing the constituents that, otherwise in the absence of beryllium, agglomerates into very visible discrete entities at 200x magnification.

Thus it has been revealed and demonstrated that the alloy of this invention, conforming in composition to A.S.T.M. B8664 Alloy XXIII and with additions of beryllium in the range .0005% to .Ol%, represents an important advance in the art with respect to zinc base die casting alloys and the die cast parts produced with the improved alloy.

It has also been revealed and demonstrated that the alloy of this invention may be modified in composition to the extent that it may contain reduced amounts of magnesium such as .005 with small additions of compensatory nickel such as .0l%.05% and copper slightly in excess of the maximum .25 such as maximum .40% and all such modified compositions with beryllium in the range .0005 %.01

This discovery alloy can be of great benefit to the zinc alloy die casting industry and to the related industries served. The availability of this discovery alloy will enable design engineers to incorporate zinc alloy die castings into machine assemblies with confidence that the limiting factor of life expectancy for the designed machine as sembly will not be the failure of the XXIII Alloy die cast parts caused by substantial loss of tensile strength after aging periods of one to fi-ve years or longer.

Tensile strength is the most significant and determinative property for cast parts to possess and every pound per square inch that can be retained during service use is of critical importance for the extension of the life of the die cast part and the machine assembly of which it is a part.

The alloy of this invention may be produced by any of the accepted methods familiar to those skilled in the art. The beryllium addition can be made either from the commercial aluminum-beryllium alloy containing approximately 5% beryllium or from a copper-aluminum-ber yllium master alloy manufactured by melting a suflicient amount of pure aluminum (25 lbs.) in a #40 or #30 graphite crucible at about 1500 F. after which a predetermined amount (30 lbs.) of 96% copper-4% beryllium alloy is added. This produces 55 lbs. of master alloy of the following composition: copper 52.3%, aluminum 45.3% and beryllium 2.37%.

The following kinds and quantities of raw materials will produce one ton of the alloy of the invention:

Pounds Zinc (special high grade 99.99+%) 1920.0 Aluminum (E.C. grade 99.8%) 78.5 Magnesium (pure stick) .4 Beryllium (Cu-Al-Be master) 4.0

A specific manufacturing procedure calls for the addition of 78.5 lbs. of pure aluminum to 1920 lbs. of pure Zinc at 900 F. After the aluminum is all in solution and with the temperature at 900 F. add 4 lbs. of the Cu-Al-Be master. This master alloy is added in small walnut sized pieces and solution is helped by gentle agitation. After the master alloy is in solution the pot is stirred, skimmed and the magnesium is added. After another stirring and skimming the pot is ready to cast.

The resultant composition will be: aluminum 4.0%, copper .10%, magnesium .02%, beryllium .004%, and the remainder zinc, with combined lead, cadmium and tin less than 012%.

If a nickel content is desired in order to produce the modified XXIII Alloy of the invention with nickel, a zinc-nickel master alloy addition or an aluminum-nickel master alloy addition can be made at the time of the aluminum addition to the zinc.

If a copper free XXIII Alloy of the invention is desired, add sufficient aluminum-beryllium master to introduce the desired amount of beryllium.

I claim:

1. A zinc base die cast alloy of high purity containing beryllium additions for imparting retention of tensile strength properties after being subjected to prolonged aging, consisting by Weight essentially of about 3.0% to about 5.0% aluminum, about 02% to about .05% magnesium, about .0005% to about 005% beryllium and the remainder zinc with iron not in excess of .10% and the combined impurities of lead, cadmium and tin not present in excess of .012% total.

2. A zinc base die cast alloy of high purity containing beryllium additions for imparting retention of tensile strength properties after being subjected to prolonged aging, consisting by weight essentially of about 3.0% to about 5.0% aluminum, about 005% to about .40% copper, about .02% to about .05% magnesium, about .0005% to about 005% beryllium and the remainder zinc with iron not present in excess of .10% and lead not present in excess of 005%, cadmium not present in excess of .004% and tin not present in excess of 003%.

3. A zinc base die cast alloy of high purity containing beryllium additions for imparting retention of tensile strength properties after being subjected to prolonged aging, consisting by weight essentially of about 3.0% to about 5.0% aluminum, about 005% to about .40% copper, about 005% to about 05% magnesium, about 005% to about .05% nickel, about .0005% to about .0l% beryllium and therernainder zinc with iron not in excess of .10% and the combined impurities of lead, cadmium and tin not present in excess of 012% total.

4. A zinc base die cast alloy of high purity containing beryllium additions for imparting retention of tensile strength properties after being subjected to prolonged aging, consisting by weight essentially of about 3.0% to about 5.0% aluminum, about .005% to about .05% magnesium, about 005% to about .05% nickel, about .0005% to about 01% beryllium and the remainder zinc with iron not in excess of .10% and the combined impurities of lead, cadmium and tin not present in excess of 012% total.

5. A zinc base die cast alloy of high purity containing beryllium additions for imparting retention of tensile strength properties after being subjected to prolonged aging consisting essentially of the following by weight:

Aluminum 3.5-4.5 Magnesium .005-.03 Beryllium .00l.005 Iron, max. .10 Lead, max. .005 Cadmium, max. .004 Tin, max. .003 Zinc Remainder 6. A zinc base die cast alloy of high purity containing beryllium additions for imparting retention of tensile strength properties after being subjected to prolonged aging consisting essentially of the following by weight:

Aluminum 3.5-4.5 Copper .005-.25 Magnesium .005.03 Beryllium .O0l-.005 Iron, max. .10 Lead, max. .005 Cadmium, max. .004 Tin, max. .003 Zinc Remainder 7. A zinc base die cast alloy of high purity containing beryllium additions for imparting rentention of tensile strength properties after being subjected to prolonged aging consisting of the following by weight:

8. A zinc base die cast alloy of high purity containing beryllium additions for imparting retention of tensile strength properties after being subjected to prolonged aging consisting essentially of the following by weight:

Aluminum '3.54.5 Magnesium .005-.03 Nickel .005-.02 Beryllium .001-.005 Iron, max .10 Lead, max. .005 Cadmium, max. .004 Tin, max. .003 Zinc Remainder 9. A zinc base die cast alloy of high purity containing beryllium additions for imparting retention of tensile strength properties after being subjected to prolonged aging consisting essentially by weight of about 3.0% to 5.0% aluminum, about 02% magnesium, about 004% beryllium and the remainder zinc with iron not in excess of .10% and the combined impurities of lead, cadmium and tin not present in excess of 012% total.

10. A zinc base die cast alloy of high purity containing beryllium additions for imparting retention of tensile strength properties after being subjected to prolonged aging consisting esentially by weight of about 3.0% to 5.0% aluminum, about .10% copper, about 02% magnesium, about 004% beryllium and the remainder zinc with iron not in excess of .10% and the combined irnpurities of lead, cadmium and tin not present in excess of 012% total.

11. A zinc base die cast alloy of high purity containing beryllium additions for imparting retention of tensile strength properties after being subjected to prolonged aging consisting essentially by weight of about 3.0% to about 5.0% aluminum, about .10% copper, about 01% magnesium, about 01% nickel, about 004% beryllium and the remainder zinc with iron not in excess of .10% and the combined impurities of lead, cadmium and tin not present in excess of 012% total.

12. A zinc base die cast alloy of high purity containing beryllium additions for imparting retention of tensile strength properties after being subjected to prolonged aging consisting essentially by weight of about 3.0% to about 5.0% aluminum, about 01% magnesium, about 01% nickel, about 004% beryllium and the remainder 9 10 zinc with iron not in excess of .10% and the combined FOREIGN PATENTS impurities of lead, cadmium and tin not present in excess 1,248,301 10/1960 France of 912% total- 1,321,677 2/1963 France.

References Cited UNITED STATES PATENTS 2,467,956 4/1949 Bierman CHARLES N. LOVELL, Primary Examiner. 3,037,859 6/1952 Larrieu 75-178 US. Cl. X.R. 3,083,096 3/1963 Larrieu 75-178 148-325 3,234,016 2/1966 Larrieu 75178 

